2-dimensional codes are symbols formed by black-and-white pattern in the coronal and transverse planes. Comparing to 1-dimensiona codes as shown in FIG. 1(a), two-dimensional bar codes possess the advantages of greater amount of information, higher density information, high reading speed, wider range of encoding, lower product cost, and strong fault-tolerance. Because of such advantages, the technology of two-dimensional codes are a topic competitively developed by all countries in the world, and widely used. Respectively, Denso Wave (reference [1]) of Japan have developed QR Code (Quick Response Code), as shown in FIG. 1(b), symbol of US have developed PDF 417 code, as shown in FIG. 1(c), and Chinese-sensible Code was developed by Chinese, as shown in FIG. 1(d).
QR Code is a 2-dimensional code formed by a back-and-white checkered pattern. QR is the short form of Quick Response, because the inventor pursued QR Code to allow its contents to be decoded quickly. QR Code is originally applied in automobile management system, then utilized for warehouse management throughout various industries. Now, following the developments of network medium and smartphones have become popular, people are relying more and more on the Internet to obtain required information. Since QR Code having excellent tracking ability of information, two-dimensional codes have been widely adopted in the marketing and advertising industries, they are commonly used for transmission of medium for advertising, two-dimensional codes can easily be accessed by scanning with a mobile phone camera.
The 2-dimensional codes referred to in this case are QR Code, and all technical parameters related to the two-dimensional code use its standard production method.
Due to the limitations of the 2-dimensional codes encoding mode, 2-dimensional codes can not present various performance randomly after the beautification processing, thus, Artists and researchers are researching a method for beautify the 2-dimensional codes. (reference [2-10]) for the purpose of visual effect and stability of encoding. Based on whether change encoding mode of 2-dimensional codes module, there are basically divided into two categories:
A first method of beautify the 2-dimensional codes is changing the encoding-algorithm of 2-dimensional code module information. The method proposed by paper (reference [11-12]), because 2-dimensional codes have fault-tolerance, even if part of the module is replaced with an image or logo, the 2-dimensional codes still can be decoded correctly. However, if the images are superimposed on the location mark or the correction mark, correct rate of decoding can be severely degrade, so, the most common method is to embed the images or symbols into the central region of the image (reference [13]), as shown in FIG. 2(a). This method limits the location of the modified module area, and the image area is only a small part of the 2-dimensional code, beautifying effect is not good enough. In addition, the code word generation process didn't be used well, deteriorating the readability of the 2-dimensional code.
The second method is for not changing the encoding-algorithm of 2-dimensional code module information, directly modifying luminance or color of the corresponding theme image. Some artists adjustment the color of 2-dimensional code to achieve artistic effects, such as shown in FIGS. 2(b) and 2(c). FIG. 2(d) is produced by Visualead (reference [14]) Online program, the method is changing the luminance of the pixels in the center of the module. Because the decoder the sampling area of the decoding region is the central region of the module, so this method can balance the decoding robustness and image fidelity. However, the proportion of the modified central pixels in the 2-dimensional code module is large, and connected Quality of images decreases. This method is not changing the encoding-algorithm of 2-dimensional code module information, guaranteeing robustness of coding, but the sampling spots of the decoding dispersed in the image, that defects have a bad influence on visual appearance.
In conclusion, A main challenge in any method of beautify the 2-dimensional codes is that the 2-dimensional codes can be decoded by standard application. The introduction of pixels results in a change in the luminance of the 2-dimensional code, the binarization threshold was twisted, and increased the probability of decoding errors. Visual optimization of the whole region of 2-dimensional code are also challenging, the error-correcting capability of 2-dimensional code has a limited, so one cannot simply replacing the image pixel with 2-dimensional codes module.
The list of references as follows:    [1] Denso Wave: http://www.qrcode.com/en/index.html    [2] LogoQstore: https://www.logoqstore.com/    [3] A.T Communications: http://logoq.net/logoq/index.html    [4] Get QR Code Generator Pro: http://www.qr-code-generator.com    [5] QRhacker.com: http://www.qrhacker.com    [6] Huaban: https://http://huaban.com/pins/756443579    [7] Frame QR: http://www.vitreoqr.com/2014/Frame_QR.html    [8] QR Pixel: http://www.qrpixel.com    [9] QR Code Artist: http://www.qrcartist.com    [10] QuickMark Color: http://color.quickmark.com.tw    [11] S. Ono, K. Morinaga, and S. Nakayama, “Two-dimensional barcode decoration based on real-coded genetic algorithm,” IEEE Congress on Evolutionary Computation, pp. 1068-1073, 2008.    [12] D. Samretwit and T. Wakahara, “Measurement of reading characteristics of multiplexed image in QR code,” International Conference on Intelligent Networking and Collaborative Systems, pp. 552-557, 2011.    [13] Unitag: https://www.unitag.io/qrcode    [14] Visualead: http://www.visualead.com    [15] Normal distribution: https://en.wikipedia.org/wiki/Normal_distribution    [16] ZXing.Net: https://zxingnet.codeplex.com    [17] G. J. Garateguy, G. R. Arce, D. L. Lau and O. P. Villarreal, “QR images: optimized image embedding in QR codes,” IEEE Transactions on Image Processing, vol. 23, no. 7, pp. 2842-2853, 2014.    [18] H. K. Chu, C. S. Chang, R. R. Lee, and N. J. Mitra, “Halftone QR codes,” ACM Transactions on Graphics, vol. 32, no. 6, pp. 217:1-217:8, 2013.    [19] W. C. Liao, “Visual arts-oriented QR code,” M.S. thesis, Yuan-Ze University, 2015.